Round 2 P2: timeoutOf() accepted ANY TimeoutReason, so under nesting — when
the upstream handed to deadline() is itself a deadline (the RFC's named
tools/execute middleware follow-up) and its outer timer fires first —
AbortSignal.any preserves the outer reason and the inner bash/web would report
the outer timeout as their own (timedOut / WEB_FETCH_TIMEOUT) though their local
timer never expired. Add an optional code to timeoutOf; bash and web pass their
own code, so a foreign timeout falls through to the upstream-cancel path.
Timeout timing/classification was re-implemented three ways across the
tool-bearing capabilities, with the fusion of timeout+cancel and the
timeout-vs-cancel reason recovery being the error-prone parts. Extract that
shared half into a zero-dependency @deepseek-ai/dsh-timeout library
(clampTimeout/deadline/timeoutOf/TimeoutReason) and leave the non-shareable
hard-kill in each capability, per the timeout-library RFC.
bash: run() owns the deadline; runBash drops its killTimer and no longer
classifies (SpawnSpec/SpawnOutcome lose timeoutMs/timedOut/aborted), so the
public timedOut/aborted booleans become mutually-exclusive first-abort
classifications. web_fetch: the hand-rolled controller/timer/listener/
signal.reason dance is replaced by provider-owned deadline/timeoutOf, keeping
the WEB_FETCH_TIMEOUT / WEB_ABORTED contract. fs stays timeout-free (README
states why).